The Small-Diameter Implant: A Valuable Treatment Option for Many Patients

Small-diameter implants (SDIs) are ideal for many patient types, providing an enriched quality of life for those who suffer from loose dentures or missing teeth but are unable to receive conventional implant therapy. With the exception of their distinctive diameters, SDIs are virtually identical to conventional-sized implants. The FDA has established 3.0 mm as the dividing line, with 3.0-mm diameter and above recognized as conventional implants, and 1.8–2.9 mm considered to be small-diameter. Like their traditional counterparts, SDIs are constructed from titanium alloy, exhibit precisely designed thread patterns, feature a surface treatment that supports osseointegration, and can be placed in an efficient, predictable and minimally invasive manner. Additionally, SDIs appear to mirror the performance capabilities of conventional-sized implants. According to multiple studies that measured the clinical outcomes of SDIs from five to 12 years, SDIs exhibit high long-term success rates.1-4 More studies will be helpful in developing and improving their diverse applications.

Function and Modality

SDIs have functioned as a beneficial treatment option for various clinical circumstances, often providing a less-invasive surgical protocol compared to conventional-sized implants. For example, patients who do not have sufficient bone for conventional-sized implants, but do have adequate bone for small-diameter implants, can receive treatment without undergoing invasive bone grafting. As such, medically compromised individuals and patients over 75 years old, who may not be able to endure extensive surgical or grafting procedures, can be ideal candidates for SDIs. In most cases, because of its minimally invasive surgical protocol, the SDI can be placed without raising a soft-tissue flap. In my experience, this results in less pain after the procedure as well as a faster healing period compared with conventional methods.

Another benefit is the speed at which the surgery and restorative procedures can be performed. Patients who are edentulous in the mandible often suffer from poor stability of their lower dentures. If the patient has adequate bone volume and density in the mandible, the clinician can place these implants in a less-invasive fashion, without an incision and the need for sutures. When SDIs achieve adequate primary stability upon insertion, a denture can be attached to the implants at the same appointment, so there’s virtually no waiting time.

Cost is another factor to consider. In one report in which 677 doctors were polled, the conventional implant surgical fee averaged between $1,700 and $1,800, compared to $760 for a small-diameter implant.5 Therefore, the cost of the surgical aspect of SDI treatment can be less than half that of conventional implants. That is an enormous advantage for patients who cannot afford the higher price tag. In addition, surgical placement of SDIs takes less time than placement of conventional implants; thus, SDIs can be more profitable and allow for increased productivity.

Placement of SDIs takes less time than placement of conventional implants.

For clinicians, particularly those new to placing implants, SDIs are a good treatment modality from a clinical and business perspective. Patients who would benefit from treatment are typically already there in the general practice, and in many cases, a short training program is all that is needed for doctors to confidently place small-diameter implants.

Treatment Planning

SDIs are especially suitable for patients with inadequate bone width for treatment with conventional-sized implants. When treatment planning an SDI case, keep in mind that on a 2-D radiograph, clinicians may be unable to distinguish whether the case would be more suitable for small-diameter implants (Fig. 1). Because this type of treatment involves the width of the bone rather than the height, the thickness of the ridge should be determined using bone calipers intraorally or with a 3-D CBCT scan.

Figure 2: Preoperative appearance of thin mandibular ridge. Patients who exhibit a thin ridge, which can be measured intraorally with bone calipers, can benefit from the minimally invasive SDI surgical protocol.

Caption

Although 3-D evaluation is ideal for diagnosis and treatment planning, it may not be realistic to ask that all patients undergo CBCT scanning prior to discussing the treatment. I’ve addressed this in my practice by first talking to the patient after visual examination and reviewing the panoramic X-ray (Fig. 2). Once I’ve determined that a conventional implant will require bone grafting but a small-diameter implant will not, for example, I discuss the treatment option with the patient. When the patient agrees to treatment, I then obtain a CBCT scan prior to performing the surgical procedure.

Surgical Protocol

For clinicians who are new to implant surgery, following the simple SDI surgical protocol can be an excellent stepping stone, especially for anyone who may be uncomfortable placing a conventional-sized implant. Once doctors are comfortable with the ease of placing SDIs, they are likely to gain the confidence needed to join the growing number of general dentists successfully placing conventional-sized implants.

In most cases, the protocol requires using a small-sized drill to puncture the superior cortical bone, which is not very thick in most cases. The clinician does not typically make an incision and raise a flap, but instead drills through the soft tissue and into the bone. When the drill reaches the softer cancellous bone, the implant is introduced into the site.

An SDI is self-tapping, meaning it can be placed without drilling to the full length of the implant (Figs. 3a, 3b). The clinician inserts the implant, and as it advances it engages bone that hasn’t been cut, thereby giving it an excellent chance of achieving high primary stability (Fig. 4). Once the implant is inserted to full depth, a torque wrench is used to measure the insertion torque, which correlates to implant stability (Figs. 5a, 5b). With SDI cases, the implants needed to support a denture can be placed in relatively quick succession (Figs. 6a, 6b).

Because only very shallow bone drilling is needed, there’s an improved chance of achieving favorable primary stability. If the primary stability is adequate, the implants can be loaded with a denture on the same day they were placed, even though biological integration has not yet occurred. The denture is stabilized by connecting to the implants via O-ring attachments that seat over the O-ball prosthetic heads of the SDIs (Figs. 7a, 7b). With good mechanical fixation and properly controlled loading, biological integration is achieved after three to six months, making the implants even more stable.

If the primary stability is adequate, the implants can be loaded with a denture on the same day they were placed, even though biological integration has not yet occurred.

A significantly shorter healing period can be expected because the clinician does not need to make an incision and raise a flap. While there are occasions in which this step is required to visualize a very thin ridge, it’s not the norm. When I place small-diameter implants for edentulous patients, over 90 percent of my cases are completed at the surgical appointment without incision and flap, meaning the patient can start to function with the stabilized denture on the first day (Figs. 8a, 8b).

Bone density is the primary factor determining whether or not the patient can use the implants immediately. However, there are methods to compensate for poor to moderate bone density in the prosthetic process. For example, Inclusive Mini Implants are available in 2.2 mm, 2.5 mm and 3.0 mm diameters (Fig. 9). One technique involves the clinician starting with a 2.2 mm implant, and if the desired initial stability is not achieved, the doctor can back that implant out and place a slightly larger-diameter implant. This provides adequate primary stability and allows for prosthetic loading on the same day in many cases.

Common Applications

SDIs support a variety of useful applications, and the most common are for the edentulous mandible and maxilla. For the edentulous arch, the rule of thumb is to place six small-diameter implants in the maxilla and four in the mandible. If a patient has a large mandible, five implants may be ideal. Small-diameter implants can also be used to stabilize partial dentures (Fig. 10).

Clinicians are not limited because of a patient’s treatment history, as implant sizes can be mixed and matched in whichever way suits the case. A common scenario presents itself when a patient has a lower denture and had previously received two conventional-sized implants in the anterior mandible, with free-standing attachments. For biomechanical reasons, there is typically lifting of the posterior of the denture during function. Of course, two implants are far better than no implants, but many patients who have two implants may not be satisfied with this level of stability. For those patients, the clinician may add one, two or three SDIs between or around the conventional-sized implants to make the denture more stable. I have successfully completed many cases of this type.

Figure 10: SDIs can be beneficial in many different applications. For example, they can be used as an affordable solution in partial denture stabilization.

Figures 11a, 11b: In select cases with limited bone volume, SDIs can be used to replace missing maxillary lateral incisors.

Figures 11a, 11b: In select cases with limited bone volume, SDIs can be used to replace missing maxillary lateral incisors.

Figure 12: An SDI can also be used to replace a missing lower incisor in cases where there is inadequate space for a conventional-sized implant, as shown in this radiograph.

Figure 13: Using an SDI between two conventional implants can dramatically reduce flexure of the fixed bridge, strain on the implants and cement failure.

Figure 14: When used to eliminate the need for a cantilever pontic in conventional implant cases, the SDI can improve biomechanics and lessen implant strain.

In addition to retaining dentures, SDIs can also be used to replace upper laterals and lower incisors (Figs. 11a, 11b). In these cases, surrounding teeth often limit the space available for implant placement. Conventional-sized implants are more difficult to fit into limited spaces, whereas a greater margin of safety can be obtained with SDIs (Fig. 12). The SDI can be restored with a variety of materials, including solid zirconia, lithium silicate ceramic and PFM.

Although less frequently performed, SDIs may be placed to support a fixed, splinted bridge connected to adjacent conventional-sized implants (Fig. 13). For example, if one or more sites have ample bone width, regular-sized implants can be placed. If the adjacent area has compromised bone width that cannot accommodate conventional-sized implants without performing grafting or creating a cantilever pontic, a small-diameter implant may be placed instead (Fig. 14). Then, the clinician can splint the SDIs and conventional implant together with a fixed bridge.

Keep in mind that SDIs can be contraindicated in some situations. For example, they should not be used in the second molar area, where significant occlusal forces are exhibited. They also should not be placed in very soft bone, such as in the maxillary posterior area.

Conclusion

FDA-cleared for long-term use, SDIs can frequently aid patients who would not otherwise receive implant treatment. These individuals may have given up hope because they needed bone grafting or a very expensive treatment that they couldn’t afford, or their health could not accommodate an invasive surgical procedure. With small-diameter implants, many patients can enjoy immediate improvement in their quality of life. It’s a rewarding experience for general dentists and a life-changing experience for patients, who express their gratitude and satisfaction instantly and commonly refer their family and friends. Because of the very simple surgical protocol that takes significantly less time than conventional implants, it’s one of the most productive and profitable procedures in my office. SDIs are a valuable and indispensable tool to add to any general dental practice.